硫化的MoO3/γ—Al2O3催化剂的表面结构和价态的研究

本文应用XPS、ESR和TEM等手段研究了硫化的MoO_3/γ-Al_2O_3催化剂样品, 在不同钼含量、不同硫化条件以及进行甲烷反应前后, 其表面结构和价态的变化规律。观察到硫化时Mo~(+6)。还原为Mo~(+5)和Mo~(+4)的变化过程。硫化除了生成S~(-2)价态外, 还有硫的高价中间态生成。证明了经甲烷化反应后, 表面上的MoS_2晶粒明显长大。

A STUDY OF VALENCE AND SURFACE STRUCTURE FOR SULFIDED MoO3/γ-Al2O3 CATALYAT

The surface structure and the valence change on sulfided MoO_3/γ-Al_2O_3 catalyst samples were investigated at different sulfidation conditions and before or after methanation reaction using XPS, ESR and TEM methods. The main results were obtained as following. The most of Mo~(+6) were easily reduced to Mo~(+4) during the samples were sulfided. Very small amount of Mo~(+5) existed and decreased when the sulfidation time was increased. More amount of Mo~(+5) was only detected by XPS on the samples of lower Mo content at lower reduction temperature and at shorter sulfidation time. The major valency of sulfur was -2 during the sulfidation proceeded. A small amount of high valence sulfur was detected and vanished during prolongation of sulfidation time. No change of the valence of Mo or S was observed after reaction for 8 hrs. It was demonstrated by TEM photogragh and diffraction pattern that MoS_2 microcrystal grew up remarkably on the sample surface after methanation reaction.